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perf_event_open.2: Clarify the PERF_FLAG_FD_* flags 

This change clarifies the behavior of the PERF_FLAG_FD_OUTPUT and
PERF_FLAG_FD_NO_GROUP flags to perf_event_open(), and removes
the related FIXME comments.

While writing tests to validate the behavior of these flags I
discovered that PERF_FLAG_FD_OUTPUT has been broken since the
2.6.35 kernel release.

Signed-off-by: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Vince Weaver 2015-01-08 12:04:30 -05:00 committed by Michael Kerrisk
parent 1fb61947c2
commit 31266c049a
1 changed files with 10 additions and 7 deletions
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17
man2/perf_event_open.2
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@ -149,14 +149,17 @@ then
.BR execve (2).
.TP
.BR PERF_FLAG_FD_NO_GROUP
.\" FIXME . The following sentence is unclear
This flag allows creating an event as part of an event group but
having no group leader.
It is unclear why this is useful.
.\" FIXME . So, why is it useful?
This flag tells the event to ignore the
.IR group_fd
parameter except for the purpose of setting up output redirection
using the
.B PERF_FLAG_FD_OUTPUT
flag.
.TP
.BR PERF_FLAG_FD_OUTPUT
This flag reroutes the output from an event to the group leader.
.BR PERF_FLAG_FD_OUTPUT " (broken since Linux 2.6.35)."
This flag re-routes the event's sampled output to instead
be included in the mmap buffer of the event specified by
.IR group_fd .
.TP
.BR PERF_FLAG_PID_CGROUP " (since Linux 2.6.39)."
This flag activates per-container system-wide monitoring.